Gesture and the processing of speech: neuropsychological evidence

Patterns of speech-related ('coverbal') gestures were investigated in three groups of right-handed, brain-damaged patients and in matched controls. One group had anomic aphasia with a primarily semantic impairment ('semantic'); one group had a primarily phonological impairment, reflected in both repetition and naming ('phonologic'); a third group had a primarily conceptual impairment, with relatively good naming ('conceptual'). Coverbal gestures were video recorded during the description of complex pictures and analyzed for physical properties, timing in relation to speech and ideational content. The semantic and phonologic subjects produced a large number of ideational gestures relative to their lexical production, while the related production of the conceptual subjects was similar to that of the unimpaired controls. The composition of ideational gestures in the semantic and phonologic groups was similar to that of the control groups, while conceptual subjects produced fewer iconic gestures (i.e., gestures that show in their form the content of a word or phrase). The iconic gestures of the conceptual patients tended to start further from their lexical affiliates than those of all other subjects. We conclude that ideational gestures probably facilitate word retrieval, as well as reflect the transfer of information between propositional and non-propositional (visual and motoric) representations during message construction. We suggest that conceptual and lexical processes differ in the way they constrain ideational gestures.